In this project we are coupling genetic study with epidemiologic, immunologic, serologic and neurochemical studies in selected families and twin pairs with disorders due to multiple factors such as multiple sclerosis, Parkinson's disease, and Alzheimer's disease. To date, 14 presumptive "Multiple Sclerosis" families and 51 twin pairs with this condition have been the subject of three publications. Sixty-five twin pairs with Parkinson's disease have been the subject of two reports. Seven twin pairs with Alzheimer's disease have been ascertained.